A whiff of putrefaction, a savour of rot, and the smell of post-mortem decay was in the air this past week as folks awaited the culmination of an eagerly-anticipated event of international significance.
I refer, of course, to the extremely rare blossoming of Amorphophallus Titanum – the infamous ‘corpse flower.’
This sort of thing doesn’t happen very often. Native to Indonesia (specifically, western Sumatra), the corpse flower, which is also known as Titan Arum, derives its popular moniker from its name in the working Malay tongue: bunga (“flower”) bangkai (“cadaver”). The name was awarded in recognition of the colossal reek that the thing emanates as part of its reproductive strategy; you might call it the ‘Drakkar Noir’ of the plant kingdom. It has been cultivated worldwide, especially in tropical botanical gardens, but there have only been about 135 flowering events outside of Sumatra in the past century. This makes the opening of the horrid, two-metre-tall blossom an event of some significance. Last weekend, for example, saw crowds flock in their thousands to gardens as far apart as Hawaii (note A) and Switzerland (note B) to witness the opening of the gargantuan flowers. You can even view the events via time-lapse photography on the internet.(note C) Perry the Corpse Flower, which resides at Gustavus Adolphus College in Minnesota, even has his own Facebook page.
Figure 1 - an Amorphophallus Titanum in all its blooming glory. Note the erect spadix, centre of the flower’s olfactory puissance
What does all this have to do with Defence, you ask? Well, the search for stench-inducing compounds – putrescent chemical agents, or ‘malodorants’ as they’re commonly known – is pretty much as old as warfare. There are sound evolutionary reasons for this. Most things that smell bad, after all, are generally also bad for you to eat, or to otherwise introduce into your body (e.g. via a puncture wound). Animals tend to shy away from the smell of rotting flesh, as this usually indicates a kill site. The purpose of malodorants is to capitalize upon ingrained responses to bad smells to convince people to voluntarily cease what they’re doing and/or leave an area, generally for riot control purposes (I mentioned this tangentially in a post last August). It also, of course, attracts creatures that prefer dead prey over live (vultures, for example). In the case of Amorphophallus, the stench serves to entice the insects that pollinate it: carrion-eating beetles and flesh flies of the family sarcophagidae (literally, “corpse-eaters”). Insect pollination, incidentally, is necessary because while both male and female flowers grow within the same inflorescence, they bloom a few days apart, preventing the thing from self-pollinating.
For humans, there is an additional layer of complexity to the problem of designing chemicals to cause aversion. Natural biological olfactory revulsion is overlain both by a significant socio-cultural matrix, and by large variances in individual responses to given odours. This makes figuring out a broad-spectrum malodorant that will be effective against everyone in a given group a challenging proposition. Researchers investigating potential candidate compounds in the US, for example, have documented widely varying responses among US test subjects from different ethnic backgrounds. Americans of recent Japanese descent, for example, appear more tolerant of human fecal odours than the average US citizen, due possibly to the centuries-old widespread use of night soil as fertilizer in a country that has traditionally had a very low domestic ovine population. At the same time, test subjects of Japanese descent seemed to be less tolerant than the average US citizen of the smell of rotting meat. This, it has been postulated, may be due to the much greater historical prevalence of meat in American than in Japanese diets.
Within such broad cultural generalizations, of course, individual preference may skew results with even greater margins of error. We all know people, for example, who are repulsed by different odours, or who seem to be more sensitive to certain smells than other people are (one explanation for the increasing prevalence of workplace posters asking folks to use sense when applying scents). Given such variation on the individual level, how is it possible to find something that, not to put too fine a point on it, is likely to make everyone sick? Well, one way is to go to the chemicals that lie at the source of the smells. Lest we imagine that this is a simple prospect, here’s a list of some of the floral volatiles that have been detected emanating from a blossoming Amorphophallus: ketones, hydroxides, nitrophenols, anisoles, acetic acid, acetophenones, pinenes, terpinolenes, benzaldehyde, beta-pinene, bicyclogermacrene, citronellol, dimethyloctadiene, E,E-alpha-farnesene, estragole, ethyl acetate, ethyl alcohol, geranial, geraniol, isohexanoic acid, limonene, methyl-butanoate, -benzoate, -butyrate and –isobutyrate, myrcene, cresols, phenylmethanol, sabinene, skatole, sulcatone, sulfanes and trimehtylheptadiene.
The flower is a literal cornucopia of complex organic compounds, some of the latter of which are the truly interesting ones. Organic sulphur compounds and skatoles have played key roles in the development of malodorant chemicals. The Israeli Defence Forces, for example, reportedly developed a riot-control mixture known as “skunk.” Based on common organic products (including yeast and baking soda), “skunk,” which replicates the odour produced by the eponymous beastie, may be dispersed as a liquid or mist, leaving rioters smelling “less than fresh.” According to at least one news article, the stench of the compound can linger in clothing for up to five years.(note D) The organic compounds in question – methyl and butyl thiols (sulphur compounds) commonly known as “mercaptans” – are also found in rotten eggs and garlic, and are produced when vulcanized rubber (which contains sulphur) is burnt. Mercaptans are some of the most potent odorants in existence, detectable by the human nose in concentrations as low as 10 parts-per-billion (ppb). For this reason, certain of these compounds (originally ethanethiol, now t-butyl mercaptan) are added to natural gas, which is naturally odourless, in order to make leaks detectable. Mercaptans are preferred for these applications because they are less dangerously reactive than other very smelly compounds, such as ammonia and hydrogen sulphide.
High-grade malodorants may have reached their zenith in two compounds produced for the US military: “US Government Bathroom Malodor”, which smells exactly like the name implies; and “Who, me?” a compound developed during the Second World War that was intended for use by resistance forces to demoralize occupying German troops, but which was allegedly discontinued because of the difficulty of dispersal (the disperser often ended up smelling as bad as the target. Self-contamination is not an unusual problem when dealing with chemicals potent in ppb concentrations). The “Bathroom Malodor” mixture actually contains some of the same volatile organic compounds given off by the corpse flower, including skatole, hexanoic acid, and various thiols. Other compounds have been tried as well.(note E) Unfortunately, a lot of the original archived documentation on malodorants once held by cbwtransparency.org is no longer available. The website closed down some years ago, and the URL has been camped by a site offering dog training tips.
The question has been raised whether malodorants constitute “chemical weapons” under the Chemical Weapons Convention. Those who argue that they do base their position on the Article II definition of “toxic chemical” as “any chemical which through its action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals.” The argument hinges on whether malodorants impact “life processes”, i.e. whether the physical revulsion resulting from exposure is a biological/physiological reaction or a purely psychological one – i.e., are you fleeing and/or vomiting not merely because you’re grossed out, but rather because the chemicals are interacting with your body chemistry? There are, after all, chemicals that will force you to vomit; they’re called “sternutators”, and have been in use since the First World War (Adamsite, aka diphenylaminechlorarsine or DM, is one example); but there is no experimental evidence to suggest that malodorant compounds actually induce a physiological reaction.
Beyond the variance in responses, perhaps the most significant complicating factor in trying to design an effective malodorant is not the legal status of the compounds, but rather the fact that personnel can become inured even to horrific smells through long exposure to the individual odorous compounds used in formulating the mixtures. This is not an uncommon animal response when acute irritants become chronic; we are adaptive creatures by nature, and can learn to put up with a surprising amount of discomfort and annoyance in order to avoid facing up to unpalatable alternatives.
All of which to say that, while our friend Amorphophallus may smell truly awful, it at least has the virtue of not lasting very long; the magnificent spadix droops, and the colossal blossom collapses and dies only 24 hours after blooming into its full, reeking majesty. Would that all irritants were as transitory.